Cancer continues to be a leading cause of mortality around the globe. Traditional regimens of cancer management have been successful in the management of a selective group of circulating and slow-growing solid cancers. However, many solid tumors are resistant to traditional approaches, and the prognosis in such cases is correspondingly grave.
One example is brain cancer. Each year, approximately 15,000 cases of high grade astrocytomas are diagnosed in the United States. The number is growing in both pediatric and adult populations. Standard treatments include cytoreductive surgery followed by radiation therapy or chemotherapy. There is no cure, and virtually all patients ultimately succumb to recurrent or progressive disease. The overall survival for grade IV astrocytomas (glioblastoma multiforme) is poor, with −50% of patients dying in the first year after diagnosis. Because these tumors are aggressive and highly resistant to standard treatments, new therapies are needed.
Another example is pancreatic cancer, the fifth leading cause of cancer-related deaths in the United States. The disease is associated with a high mortality rate, with a medium survival for untreated patients after diagnosis of about 4 months. Ninety percent of pancreatic cancer patients initially present with locally advanced, surgically unresectable disease. Current therapy for these patients is strictly palliative and does not significantly impact on overall patient survival. Most recently, the chemotherapeutic agent, Gemcitabine (GEMZAR™) was shown to improve overall median survival to 5.7 months compared to that of 5-fluorouracyl (4.2 months) and had a better clinical benefit index. However, it is clear that even with these newer agents, palliation of the disease is highly temporary.
An emerging area of cancer treatment is immunotherapy. There are a number of immunological strategies under development, including: 1. Adoptive immunotherapy using stimulated autologous cells of various kinds; 2. Systemic transfer of allogeneic lymphocytes; 3. Vaccination at a distant site to generate a systemic tumor-specific immune response; 4. Implantation of immune cells directly into the tumor.
The first of these strategies, adoptive immunotherapy, is directed towards providing the patient with a level of enhanced immunity by stimulating cells ex vivo, and then readministering them to the patient. The cells are histocompatible with the subject, and are generally obtained from a previous autologous donation.
One version is to stimulate autologous lymphocytes ex vivo with tumor-associated antigen to make them tumor-specific. Zarling et al. (1978) Nature 274:269-71 generated cytotoxic lymphocytes in vitro against autologous human leukemia cells. In U.S. Pat. No. 5,192,537, Osband suggests activating a tumor patient's mononuclear cells by culturing them ex vivo in the presence. of tumor cell extract and a non-specific activator like phytohemagglutinin or IL-1, and then treating the culture to deplete suppresser cell activity. Despite these experimental observations, systemic administration of ex vivo-stimulated autologous tumor-specific lymphocytes has not become part of standard cancer therapy.
Autologous lymphocytes and killer cells may also be stimulated non-specifically. In one example, Fc receptor expressing leukocytes that can mediate an antibody-dependent cell-mediated cytotoxicity reaction are generated by culturing with a combination of IL-2 and IFN-γ (U.S. Pat. No. 5,308,626). In another example, peripheral blood-derived lymphocytes cultured in IL-2 form lymphokine-activated killer (LAK) cells, which are cytolytic towards a wide range of neoplastic cells, but not normal cells. In combination with high dose IL-2, LAK cells have had some success in the treatment of metastatic human melanoma and renal cell carcinoma. Rosenberg (1987) New Engl. J. Med. 316:889-897. For examples of trials conducted using LAK in the treatment of brain tumors, see Merchant et al. (1988) Cancer 62:665-671 & (1990) J. Neuro. Oncol. 8:173-198. While not associated with serious clinical complications, efficacy is typically only anecdotal or transient
Another form of adoptive therapy using autologous cells has been proposed based on observations with tumor-infiltrating lymphocytes (TIL). TILs are obtained by collecting lymphocyte populations infiltrating into tumors, and culturing them ex vivo with IL-2. TILs have activity and tumor specificity superior to LAK cells, and have been experimentally administered, for example, to humans with advanced melanoma. Rosenberg et al. (1990) New Engl. J. Med. 323:570-578. Unfortunately, TILs can only be prepared in sufficient quantity to be clinically relevant in a limited number of tumor types, and remain experimental.
The second of the strategies for cancer immunotherapy listed earlier is adoptive transfer of allogeneic lymphocytes. The rationale of this experimental strategy is to create a general level of immune stimulation, and thereby overcome the anergy that prevents the host's immune system from rejecting the tumor. Strausser et al. (1981) J. Immunol. Vol. 127, No. 1 describe the lysis of human solid tumors by autologous cells sensitized in vitro to alloantigens. Zarling et al. (1978) Nature 274:269-71 demonstrated human anti-lymphoma responses in vivo following sensitization with allogeneic leukocytes. Kondo et al. (1984) Med Hypotheses 15:241-77 observed objective responses of this strategy in 20-30% of patients, and attributed the effect to depletion of suppressor T cells. The studies were performed on patients with disseminated or circulating disease. Even though these initial experiments were conducted over a decade ago, the strategy has not gained general acceptance, especially for the treatment of solid tumors.
The third of the immunotherapy strategies listed earlier is the generation of an active systemic tumor-speck immune response of host origin by administering a vaccine composition at a site distant from the tumor.
Various types of vaccines have been proposed, including isolated tumor-antigen vaccines and anti-idiotype vaccines. Another approach is to use tumor cells from the subject to be treated, or a derivative of such cells. For review see, Schirrmacher et al. (1995) J. Cancer Res. Clin. Oncol. 121:487-489. In U.S. Pat. No. 5,484,596, Hanna Jr. et al, claim a method for treating a resectable carcinoma to prevent recurrence or metastases, comprising surgically removing the tumor, dispersing the cells with collagenase, irradiating the cells, and vaccinating the patient with at least three consecutive doses of about 107 cells.
In yet another approach, autologous or syngeneic tumor cells are genetically altered to produce a costimulatory molecule. For reviews see, Pardoll-et al. (1992) Curr. Opin. Immunol. 4:619-23; Salto et al. (1994) Cancer Res. 54:3516-3520; Vieweg et al. (1994) Cancer Res. 54:1760-1765; Gastl et al. (1992) Cancer Res. 52:6229-6236; and WO 96/07433. Tumor cells have been genetically altered to produce TNF-α, IL-1, IL-2, IL-3, IL-4, IL-6, IL-7, IL-10, IFN -α, IFN-γ and GM-CSF.
PCT Publication No. WO 98/16238 describes cancer immunotherapy using autologous tumor cells combined with allogeneic cytokine-secreting cells. The vaccines comprise a source of tumor-associated antigen, particularly tumor cells from the patient to be treated, combined with an allogeneic cytokine-secreting cell line. Exemplary cytokines are IL-4, GM-CSF, IL-2, TNF-α, and M-CSF in the secreted or membrane-bound form. The cytokine-producing cells provide immunostimulation in trans to generate a specific immune response against the tumor antigen. Vaccines can be tailored for each type of cancer or for each subject by mixing tumor antigen with an appropriate number of cytokine-producing cells, or with a cocktail of such cells producing a plurality of cytokines at a favorable ratio.
The fourth of the immunotherapy strategies listed earlier is intra-tumor implantation, directed at delivering effector cells directly to the site of action. The proximity of the effector cells to the target is supposed to promote the ability of the transplanted cells to react with the tumor, generating a graft versus tumor response.
Kruse et al. (Proc. Natl. Sci. USA, 87:9377-9381, 1990) analyzed various effector cell populations in adoptive immunotherapy of the 9L rat gliosarcoma cell line. Different cell populations were prepared that were designed to have a direct effector function—against the cancer cells. Included were syngeneic lymphocytes, nonadherent lymphocyte-activated killer (LAK) cells, adherent LAK cells, syngeneic cytotoxic T lymphocytes (CTL) raised against tumor antigens, and allogeneic CTL raised against alloantigens. The allogeneic cytotoxic T lymphocytes were claimed to prevent tumor take. The CTL were prepared by coculturing thoracic duct lymphocytes from one inbred rat strain with spleen cells from rats syngeneic to the challenged animals, under conditions and for a period designed to enrich for cytotoxic effector cells. Treatment was effected by coinjecting the CTL with the tumor cells into the brains of rats in conjunction with recombinant IL-2, and then readministering the CTL on two subsequent occasions. The regimen was claimed to forestall tumor take by 17 days. The authors state that the tumor is successful in the brain, because the brain is an immunologically privileged site which prevents the administered cells from being eliminated before they perform their function. A corollary of this is that the treatment would not be effective at other sites (such as the pancreas and the breast) that are not immunologically privileged.
In a subsequent study, Kruse et al. (J. Neuro-Oncol, 19:161-168, 1994) performed intracranial administrations of single or multiple source allogeneic cytotoxic T lymphocytes. In this study, the 9L cancer cell line was injected into rats only 6 days before the initiation of treatment. A series of four injections of allogeneic T lymphocytes within the next 17 days was performed, and had the effect of extending the median life span of the rats by 19 days (about the same interval as the treatment protocol). There is no evidence for any lasting effect, despite the fact that four doses of the effector cells are given. This is consistent with the author's hypothesis that the tumoricidal effect is generated by the CTL themselves, and disappears once the administered cells are eliminated.
Two other publications by the same group demonstrates the natural progression of this CTL implantation technology in a direction towards greater enrichment for cells with a direct effector action against the tumor.
J. M. Redd, et al. Cancer Immunol. Immunother., 34:349, 1992 describe a method of generating allogeneic tumor-specific cytotoxic T lymphocytes. CTL were generated in culture from an inbred rat strain allogeneic to the tumor cell line. The cells were found to lyse both tumor cells and Con A stimulated lymphoblasts of the same tissue type. The tumor-specific subset was deliberately selected and enriched as being specific for a determinant expressed only by the tumor. The article concludes by stating that the ultimate goal of the authors is to transfer the technology to humans using allogeneic CTL lacking specificity for normal brain antigens (i.e., depleted of alloreactive cells). This is a significant elucidation of the previous article by Kruse et al. in Proc. Natl. Acad. Sci. (supra, p. 9579 col. 1), in which they refer to two types of allogeneic CTL, one of which is tumor specific and one of which is allospecific. The yield of tumor specific cells was substantially lower. The article by Redd et al. teaches that the tumor specific cells are preferred, and provides a way of enriching for them when using cultured rat cells.
More recently, Kruse et al. (Proc. Am. Assoc. Cancer Res. 36:474, 1995; FASEB J. 10:A1413, 1996) briefly outline a clinical study of human brain cancer patients. The patient's lymphocytes were expanded with OKT3 and IL-2, then co-cultured with allogeneic donor cells for 18-21 days in the presence of IL-2. Such culture conditions would result in a population highly enriched for terminally differentiated effector cells. Patients enrolled in the Phase I study received CTL into the tumor bed and were placed with a catheter for subsequent infusions. Ongoing treatment involved 1 to 5 treatment cycles every other month, with each cycle consisting of 2-3 CTL infusates within a 1 to 2 week period. Again, the ongoing necessity to readminister the cells is consistent with the author's stated objective of providing cells with a direct cytolytic effect on the tumor.
The necessity of ongoing repeated administration of the effector cells to the tumor through a cannula severely limits the practical utility of this technology, both in terms of expense and the inconvenience to the patient.
In view of the limitations of may of these strategies, new approaches to the treatment of cancer are needed.
Considerable progress was made towards a simpler and more effective immunotherapeutic strategy by the development of cytoimplants. See PCT Publication No. WO 96/29394, a “Method for Treating Tumors”. Potent cellular compositions are placed directly into the tumor bed, leading to beneficial effects for patients with different types of cancers. The method can be conducted as follows: The tumor patient's leukocytes are co-cultured in a mixed lymphocyte cell reaction with healthy lymphocytes derived from an allogeneic donor. The alloactivated cells are surgically implanted at the tumor site, and produce a mixture of cytokines which induce a primary immune response. During this reaction, the host lymphoid cells identify both the graft lymphoid cells and tumor tissue as foreign.